Earlier this year, the price of the electronic currency Bitcoin exploded upwards, making its early advocates rich and smug and leaving everyone else shouting "bubble!" Then, the price of Bitcoin crashed, making everyone who had cried "bubble" feeling smart and smug. And then, a few weeks ago, the price of Bitcoin started exploding again. And, so, once again, Bitcoin believers are crowing, and everyone else is mumbling about "bubbles." So, who's right? Most likely, everyone. Why? Because Bitcoin is the perfect asset bubble. There is absolutely no way to value Bitcoin, which means there is nothing constraining its price other than supply and demand. As long someone new can be convinced to buy Bitcoin, its price can keep rising. Bitcoin prices could literally go to 1,000 or 10,000 or 100,000 or 1 million per coin, and there would be no way to prove that these prices were ridi...